Atrial fibrillation (AF) is the most common arrhythmia in humans and represents a significant public health problem. There are presently 2.2 million cases of AF in the United States and approximately 160,000 new cases diagnosed each year. AF is typically managed by a combination of anti-arrhythmic drugs and external or internal electrical cardioversion. In addition, surgical compartmentalization or radiofrequency ablation of atrial tissue can be used. Unfortunately, long term success rates are low; AF recurrence is high with both drug treatment and electrical cardioversion with internal and external shocks.
Internal electrical cardioversion of AF remains an uncomfortable therapy option for managing patients with AF. Even with recent advancements, shock voltages necessary to defibrillate the atrial, while considerably lower than that for the ventricles, are still beyond the pain threshold. One reason high voltages may be necessary is that the main generator for AF is the left atrium and direct access to the left atrium is problematic because of the risk of embolism. Typically, atrial defibrillation lead locations are limited to right sided chambers (right atrium and right ventricle) and venous structures accessible from the right side of the heart (coronary sinus).
To creat a trans-atrial shocking vector, the most common approach is to shock between one or more electrodes on the right side of the heart (right atrial appendage, superior vena cava, or right ventricle) to an electrode on the left side of the heart in the distal coronary sinus. The left atrium is also an important atrial chamber to defibrillate since (i) it can fibrillate independent of the right atrium, (ii) mapping studies have shown that earliestsites of activation following failed defibrillation arise from the left atrium for most defibrillation electrode configurations, (iii) early sites in or near the pulmonary veins have been shown to be responsible for the initiation of and early reoccurence of AF in many patients, and (iv) ablation of right atrial structures alone has had poor success in terminating AF or preventing its reoccurence. Nevertheless, there remains a need for means of defibrillating the atria of a subject without unduly high energy defibrillation pulses that would be painful to the subject being treated.